The present disclosure relates generally to electronic deadman/autoshear circuits. More specifically, in certain embodiments the present disclosure relates to deadman/autoshear circuits used in blowout preventers and associated methods.
Considerable safety measures are often required when drilling for oil and gas on-shore and off-shore. One such safety measure is the use of blowout preventers (BOPs). BOPs are basically large valves that close, isolate, and seal wellbores to prevent the discharge of pressurized oil and gas from the well during a kick or other event. One type of BOP used extensively is a ram-type BOP. This type of BOP uses opposing rams that close by moving together to either close around the pipe or to cut through the pipe and seal the wellbore.
The blowout preventers are typically operated using pressurized hydraulic fluid to control the position of the rams. Most BOPs are coupled to a fluid pump or another source of pressurized hydraulic fluid. In most applications, multiple BOPs are combined to form a BOP stack, and this may include the use of multiple types of BOPs. In some applications, a first ram of a BOP stack may be activated to shear the drill pipe and then subsequent rams may be operated to further seal the well bore once the drill pipe has been removed from the path of the subsequent rams.
In this case of multiple rams, it is often desirable to have a delay between the activation of the shearing ram and the activation of the sealing rams. Currently in the industry, this delay may be achieved by the use of a timing cylinder. Briefly, once the shearing ram is activated, hydraulic fluid may be allowed to fill into a piston cylinder pressurizing it until it reaches a pressure that is capable of actuating the secondary rams. Then the sealing rams are activated and the wellbore is effectively sealed. Other methods of sequencing the closure of multiple BOP shear rams rely on hydraulic timing circuits.
While such timing cylinders and circuits have been useful, they may suffer from several deficiencies. The timing cylinders and circuits may not always produce consistent or repeatable time intervals between the completion of the first shear ram function and the activation of the second shear ram function because they rely on hydraulic pressure and flow rates for timing. These inconsistent time intervals may results in the drill pipe still being in the path of the sealing rams when they are activated thus preventing the sealing of the well bore, late sealing of the wellbore or incomplete sealing of the wellbore.
It is desirable to develop a method and apparatus for sequentially activating blow out preventers that does not suffer the drawbacks of conventional methods.